Core-flow represents the pumping through a pipeline of a viscous liquid such as oil or an oil emulsion, in a core surrounded by a lighter viscosity liquid, such as water, at a lower pressure drop than the higher viscosity liquid by itself. Core-flow may be established by injecting the lighter viscosity liquid around the viscous liquid being pumped in a pipeline. Any light viscosity liquid vehicle such as water, petroleum and its distillates may be employed for the annulus, for example fluids insoluble in the core fluid with good wettability on the pipe may be used. Any high viscosity liquid such as petroleum and its by-products, such as extra heavy crude oils, bitumen or tar sands, and mixtures thereof including solid components such as wax and foreign solids such as coal or concentrates, etc. may be used for the core.
Friction losses may be encountered during the transporting of viscous fluids through a pipeline. These losses may be due to the shear stresses between the pipe wall and the fluid being transported. When these friction losses are great, significant pressure drops may occur along the pipeline. In extreme situations, the viscous fluid being transported can stick to the pipe walls, particularly at sites that may be sharp changes in the flow direction.
To reduce friction losses within the pipeline, a less viscous immiscible fluid such as water may be injected into the flow to act as a lubricating layer for absorbing the shear stress existing between the walls of the pipe and the fluid. This procedure is known as core flow because of the formation of a stable core of the more viscous fluid, i.e. the viscous oil, and a surrounding, generally annular, layer of less viscous fluid.
Core flow may be established by injecting the less viscous fluid around the more viscous fluid being pumped in the pipeline.
Although fresh water may be the most common fluid used as the less viscous component of the core flow, other fluids may be used.
The world's easily found and easily produced petroleum energy reserves are becoming exhausted. Consequently, to continue to meet the world's growing energy needs, ways must be found to locate and produce much less accessible and less desirable petroleum sources. Wells may be now routinely drilled to depths which, only a few decades ago, were unimagined. Ways are being found to utilize and economically produce reserves previously thought to be unproducible (e.g., extremely high temperature, high pressure, corrosive, acidic, sour, and so forth). Secondary and tertiary recovery methods are being developed to recover residual oil from older wells once thought to be depleted after primary recovery methods had been exhausted.
Some reservoir fluids have a low viscosity and may be relatively easy to pump from the underground reservoir. Others have a very high viscosity even at reservoir conditions. Others have a high acidity which may be corrosive to tubulars, pumping equipments, and later to refinery equipment.
Electrical submersible pumps may be used with certain reservoir fluids, but such pumps generally lose efficiency as the viscosity of the reservoir fluid increases.
If the produced crude oil in a well has a high viscosity for example, viscosity from about 200 to about 2,000,000 (centiPoise) cP, then friction losses in pumping such viscous crudes through tubing or pipe can become very significant. Such friction losses (of pumping energy) may be due to the shearing stresses between the pipe or tubing wall and the fluid being transported. This can cause significant pressure gradients along the pipe or tubing. In viscous crude production such pressure gradients cause large energy losses in pumping systems, both within the well and in surface pipelines.
U.S. Pat. No. 5,159,977, discloses that the performance of an electrical submersible pump may be improved by injection of water such that the water and the oil being pumped flow in a core flow regime, reducing friction and maintaining a thin water film on the internal surfaces of the pump. U.S. Pat. No. 5,159,977 is herein incorporated by reference in its entirety.
Co-pending patent publication WO 2006/132892, discloses a system adapted to transport two fluids and a gas comprising a nozzle comprising a first nozzle portion comprising the first fluid and the gas, and a second nozzle portion comprising the second fluid, wherein the second nozzle portion has a larger diameter than and is about the first nozzle portion; and a tubular fluidly connected to and downstream of the nozzle, the tubular comprising the first fluid and the gas in a core, and the second fluid about the core. Co-pending patent application WO 2006/132892 is herein incorporated by reference in its entirety.
Patent application MX2005PA007911 discloses a process for reducing naphthenic acidity in petroleum oil or its fraction comprises: providing the oil supply (0.1-99 wt. %) in water that is emulsified/dispersed in the oil, where the oil contain salts and naphthenic acid content is 0.1-10 mg that are measured by total acid number (TAN) measurement using KOH/g; sending the oil with the water towards a device, which is emitting microwave radiation, where the oil is subjected under the microwave radiations in liquid phase at 50-350 deg. C. under 0.7-4.5 MPa in which the microwave radiations have influencing distance of 1 mm-30 cm of the oil, in the presence of salts, applied temperature and the high permittivity of the water droplets involve absorption of heat preferably heating water in the place of oil, the naphthenic compounds interface between the droplets, and the oil absorb the heat; decomposing carboxylic acids (that is responsible for naphthenic acidity) of 320 deg. C. to liberate CO2; separating the formed gas, water and oil phases using a separating device; and recovering the oil having reduced amount of naphthenic acids. The process is applied for reducing naphthenic acid in oil or its fractions during the oil production-phase performed in refineries or any other industrial facility. Patent application MX2005PA007911 is herein incorporated by reference in its entirety.
There is a need in the art to provide economical, simple techniques for moving viscous fluids in a tubular.